The present invention pertains to a method for the early detection of sunburn, to an auxiliary means for the early detection of sunburn, as well as to a method for determining a suitable transmission, reflection or emission spectrum of an auxiliary means.
Interest has been increasingly focused in the past years on research into the effects of UV rays on humans. An excessively intense irradiation of the skin with UV light leads, among other things, to sunburn in humans. Signs of sunburn also include tenderness and functional impairment, besides reddening, swelling and overheating of the irradiated skin area. These reactions are signs of an inflammation, as a consequence of which damage to the epidermal cells may develop. Mediators, including prostaglandins, which lead to a dilatation of the blood vessels and to painful burning in the case of sunburn, are released in the process. The immigration and cytolysis of numerous cells occur during the further course. Besides these temporary consequences of a sunburn, permanent skin damage may also occur, depending on the intensity of the irradiation and the sensitivity of the particular person, e.g., due to a change in the genetic information in the cell nucleus, which may cause skin cancer in the worst case.
Since the ozone layer filters UVB and UVC components out of the natural solar radiation, increasing amounts of this radiation reach the surface of the earth as the ozone layer is increasingly destroyed. In addition, man is increasingly frequently exposed to natural UV radiation in the form of sunlight or natural UV radiation in solaria in order to meet the ideal of beauty of a tanned body. An increase in the number of cases of skin cancer was able to be observed in the wake of these developments.
It has now been ascertained that there is a direct relationship between the radiation dose to which a person is exposed and the probability of developing skin cancer.
To prevent skin damage as a consequence of sunburn, a certain UV radiation dose must not be exceeded within a certain time interval. The radiation dose that is currently still considered to be medically acceptable is the radiation dose that leads to a visible red coloration after 24 hours and is called the minimal erythema dose (MED). The value of this dose depends on the skin type and the pretanning of the person.
The fundamental problem in avoiding sunburn is the time delay with which the signs of sunburn appear after irradiation. Since the inflammation reaches its maximum only about 24 hours after the irradiation, it is not sufficient to avoid sunlight after the first reddening of the skin is observed in order to avoid a sunburn because the medically harmless radiation dose had already been exceeded by that time. A further irradiation going beyond the harmless MED radiation should rather be avoided already at the time at which an incipient sunburn is not yet perceptible.
To determine this point in time, a method and a device, with which it can be determined how long a person can still continue to be exposed to UV irradiation without damage have been known from WO 93/16635 and U.S. Pat. No. 4,882,598. A skin area is irradiated and its reflection is subsequently measured here. Based on these values, a reflection coefficient can be determined, which can be assigned to a certain degree of reddening of the skin. The drawback of this procedure is the complicated measuring means and evaluation of the measurement results, so that the method and the device are unsuitable for the common use, e.g., during tanning.
In addition, it has been known from U.S. Pat. No. 4,432,736 that the intensity of the reddening of the skin and thus the intensity of the sunburn can be inferred from the specific reflection spectrum of irradiated skin areas. The method disclosed there is, however, limited to an exact determination of the remission spectrum with subsequent evaluation of the reflection curve. The fact that a complicated apparatus, by means of which the remission spectrum is first determined and subsequently evaluated, is needed to detect the remission spectrum is a drawback in this case as well. Thus, a complicated apparatus and a time-consuming procedure are consequently needed to obtain information on the degree of sunburn, and this approach is therefore rather impractical.
Furthermore, it has been known from DE 31 37 326 A1 that the degree of tanning of the human skin can be determined by means of a device in which the skin is exposed to a light source of a defined spectral composition and the light is again received by a light sensor. This arrangement is tailored to and at the same time limited to the determination of the degree of tanning of the human skin. The tanning of human skin depends on the melanin content in the skin and begins only after a sunburn. Thus, it is not possible to predict a sunburn to be expected.
Finally, it has been known from DE 34 19 872 A1 that the coloring of the skin as a consequence of solar radiation can be determined by means of logically ordered color carriers. Even though the instantaneous state of the color of the skin can thus be determined, a sunburn is noticed in the manner disclosed in DE 34 19 872 A1 only after it has occurred because the red coloration as a consequence of sunburn follows the irradiation with a time delay only and reaches its maximum approx. 24 hours after the irradiation. Thus, this device is not suitable for avoiding sunburn.
Against this background, the basic object of the present invention is to provide a reliable, easy-to-handle and effective method for the early detection of a sunburn as well as a corresponding auxiliary means therefor.
The present invention is based on the discovery that the UV irradiation of the skin leads to skin changes, e.g., the accumulation of hemoglobin and oxyhemoglobin in the near-surface layers of the skin. Based on the characteristic absorption behavior of these substances, the reflection spectrum of the skin is changed to the extent that a sunburn is perceived as reddening of the skin beginning from a certain degree of change. A certain reflection spectrum can be graphically assigned to each grade of reddening of the skin, and any change in the shade thus brings about a changed reflection spectrum.
In addition, it has been recognized that the change in the reflection spectrum and thus the intensity of the reddening or the extent of the sunburn will still increase even when there is no further irradiation. The maximum of this development is reached after about 24 hours. It is also assumed in the present invention that the change in the red coloration of the skin over time as a function of the UV radiation dose is known and is essentially the same within certain limits.
As was already mentioned, a medically harmless radiation dose, which just does not yet lead to any skin damage, can be assigned for each person depending on his or her skin type. This dose can be determined experimentally and leads to a just visible red coloration of the skin after about 24 hours, after the sunburn shows its maximum effects. Typical reflection spectra, which describe the characteristic course of the reddening of the skin in the case of a sunburn, can be assigned to this radiation dose, also called MED, as a function of time. Of this large number of reflection spectra, precisely the spectrum at the time of the end of the irradiation is significant for the present invention, because this spectrum indicates unambiguously when a person must stop being exposed to further radiation if the delayed skin reaction should not lead to any more damage.
The insufficient color sensitivity of the human eye is a problem in utilizing this discovery. A shade is determined basically by the mixing ratio with which individual spectral ranges come together. If all spectral ranges are changed uniformly, this does not affect the mixing ratio, i.e., the shade remains the same, and only the lightness is changed. If, by contrast, only individual spectral ranges are changed, this leads to a change in the mixing ratio, which can lead to a change in the shade. However, the human eye can perceive a significant change in shade only when the change exceeds a certain threshold value.
The addition of different spectral components of the non-irradiated skin leads to the perception of a shade typical of the skin in the human eye. Due to the increasing concentration of hemoglobin and oxyhemoglobin as a consequence of UV irradiation, there is increased absorption of spectral components in the wavelength ranges from 400 to approx. 630 nm. This leads to reduced reflection of the light in these wavelength ranges, so that the shade perceptible to the human eye is composed of another mixing ratio of the different spectral ranges. However, this leads to a perceptible red coloration of the skin, which becomes increasingly intense with increasing concentration, only beginning from a certain threshold concentration of hemoglobin and oxyhemoglobin. Even though the reflection spectrum of the skin is changed below the threshold concentration, the change is not perceptible to the human eye as a color change to red. The reflection spectrum that indicates that the MED radiation has been reached and thus shows that more radiation should be avoided also falls within this range, which is still imperceptible to the naked eye. This spectrum will hereinafter be called the borderline spectrum.
Thus, the person is unable to detect this slight change in the shade of the skin until the just still tolerable radiation dose is reached without suitable auxiliary means.
The present invention makes this borderline spectrum visible, which does not yet lead to a color change of the skin when viewed with the naked eye in daylight, directly to the eye. This is achieved by selectively changing the borderline spectrum over at least part of the entire spectral range, where wavelength ranges from 620 nm to 700 nm possibly remain unchanged, whereas the other wavelength ranges from 400 to 620 nm are absorbed to an increased extent.
If the spectrum of the auxiliary means according to the present invention is correspondingly adapted, a clearly perceptible color change can be achieved when a certain reflection spectrum of the skin is reached when viewing the skin with a light to be specified (sunlight or artificial light).
The advantage of the present invention is that a simple and yet reliable method and auxiliary means have been created for the early detection of sunburn, which method can be carried out without a complicated device. The method can be correspondingly carried out and the device can be manufactured at an extremely low cost and they are thus accessible to many users.
The user obtains the result of the examination immediately and without complicated evaluation by means of reference curves, reference areas or charts. Possible sources of error are thus avoided and the reliability of the present invention is at the same time increased.
The examination of the skin is not linked with any discomfort because it is carried out in a completely contactless manner. Free movement is possible during the examination and the result is obtained immediately. Even an examination performed from a distance yields reliable results. This is advantageous especially in the case of supervising children, in whom a sunburn causes damage sooner than adults and who should therefore be checked for signs of a sunburn especially frequently.
Another advantage of the present invention is its independence from the skin type and the skin color. What is decisive for the method according to the present invention is the appearance of a certain reflection spectrum, which is made visible by a color change. This reflection spectrum is caused by a certain radiation dose, which may be different for different skin types and skin colors, but it always leads to sunburn when it is reached. This means that even though people with different skin types or skin colors can expose themselves to an equal UV radiation over different lengths of time, they should stop being exposed when a red coloration visible with the auxiliary means has been reached in order to avoid skin damage.
A preferred embodiment of the present invention is a filter with a corresponding transmission spectrum, because a filter can be manufactured and handled in an extremely simple manner. In addition, there are situations in which an auxiliary means meaningfully comprises a reflecting surface with a corresponding remission spectrum, e.g., a mirror. Such a case would occur, e.g., when one would like to detect a beginning sunburn in the face himself. Daylight is a suitable light source for the irradiation, but the auxiliary means may also be designed for viewing in artificial light.
Technically more complicated but just as reliable in operation is the use of a light source with a corresponding emission spectrum. A light source according to the present invention has increased emission in the red range compared with the other spectral ranges.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.